The present invention relates to electric motor braking systems. More specifically, the present invention is concerned with an anti-rollback system and method for an electric motor.
On most electric vehicles such as wheelchairs, braking is provided by a controller that commands the voltage supply on the electric motor so as to bring the vehicle to a stop. Such vehicles are further provided with a secondary brake that ensures the immobility of the vehicle once the voltage is removed from the motor. The secondary brake is usually mechanical.
A common problem to most electric vehicles is the so-called rollback, i.e. the small unwanted backward movement of the vehicle that occurs when the vehicle stops or starts while the vehicle is on a slope. Indeed, when a conventional electric vehicle that is climbing a slope is commanded to stop via an input device, it first stops and then goes backwards over a short distance before coming to a full stop. Similarly, when the electric vehicle starts again, it first goes backward before moving forward. Obviously, xe2x80x9crollbackxe2x80x9d also occurs in a descent in the form of a short period free-fall.
Even though malfunctions of the braking system of an electric vehicle are uncommon, rollback may bring a feeling of insecurity to the passenger.
The PCT application No. 99/02363 published on Jan. 21, 1999 naming Pugh as the inventor, and entitled xe2x80x9cBrake Control Apparatus and Methodxe2x80x9d describes a brake control apparatus and method for an electric vehicle.
The Pugh apparatus includes an electric motor current monitor and a controller that controls the voltage applied to the motor, the braking force applied to the brakes, and also determines the time that the control voltage and the braking force are applied.
According to Pugh, to stop the electric vehicle, the brakes are triggered when the voltage demand of the electric motor reaches zero. However, Pugh does not take into account the fact that most mechanical brakes have a delay between their triggering and their full operation. This delay, added to the fact that the brakes are only triggered when no voltage is applied to the motor, may be the cause of rollback.
Moreover, when determining the triggering time for the control voltage and the braking force, Pugh does not take into account the current environmental temperatures and the motor wear. This may cause additional delay and increase the residual rollback effect.
More specifically, in accordance with the present invention, there is provided a method for managing the stopping of a wheel driven by an electric motor using a secondary brake, the method comprising:
providing the secondary brake application time;
upon receiving a stop triggering signal:
controlling the electric motor so as to bring the wheel to a stop;
applying the secondary brake;
waiting at least a period of time corresponding to the secondary brake application time while collecting data related to the voltage applied during the braking and removing voltage from the electric motor,; and
upon receiving a start triggering signal:
using the collected data to apply on the electric motor about the voltage applied during braking;
removing the secondary brake; and
controlling the electric motor so as to bring power to the wheel.
According to a second aspect of the present invention, there is provided a system for managing the stopping of a wheel driven by an electric motor, the system comprising:
a controller to be connected to the electric motor;
a secondary brake for selectively stopping the wheel; the secondary brake having a brake application time;
a monitoring device connected to both the controller and the electric motor;
the controller being configured for,
upon receiving a stop triggering signal:
controlling the electric motor so as to bring the wheel to a stop;
applying the secondary brake;
waiting at least a period of time corresponding to the secondary brake application time while collecting data related to the voltage applied during the braking and removing voltage from the electric motor,; and
upon receiving a start triggering signal:
using the collected data to apply on the electric motor about the voltage applied during braking;
removing the secondary brake; and
controlling the electric motor so as to bring power to the wheel.
Other objects, advantages and features of the present invention will become more apparent upon reading the following non restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings.